The present invention relates to electrophoretic deposition and, more particularly, to a method for the electrophoretic deposition of monolithic and laminated ceramic bodies coated with a layer of glass and shaped as dental appliances for dental restorations. Most specifically, the present invention relates to electrophoretic deposition of layers or composite of ceramic and glass particles to produce metal-free dental appliances, such as, but not limited to, crowns, artificial teeth and bridges, on a duplicate dental die obtained from a master model.
Precisely shaped, small ceramic bodies are used in many applications, including as pitch bonding capillaries in microelectronics, as high temperature nozzles, as ferrules for connecting optical fibers, as high temperature engine components, as dental appliances such as dental crowns, artificial teeth and bridges and as bearing parts.
To achieve the precise shaping required, some of these applications, e.g., bonding capillaries, it has been necessary to use the process of cold pressing to fabricate ceramic capillaries. To produce all-ceramic dental appliances a manual slip cast process is presently excercised.
Multilayer ceramic laminates, made of sequential layers of ceramics such as alumina and zirconia, are known in a variety of geometric shapes, including plates and discs. Applications of ceramic laminates include mechanical seals, automotive engine parts, furnace elements, multilayer and FGM substrates for hybrid circuits, capacitors, RF filters, and microwave components.
The processes used to fabricate ceramic laminates include chemical vapor deposition (CVD) and physical vapor deposition (PVD), for layers less than few microns in thickness; tape casting, for layers thicker than about 10 microns; and electrophoretic deposition (EPD), for layers between about 3 micron and about 100 microns in thickness, as will now be described.
Electrophoresis is a process in which charged ceramic particles suspended in a liquid medium are attracted to an electrode when an electrical field is imposed on the particles. EPD is the process of depositing a body of a desired shape on an electrode, using electrophoresis. EPD has long been used to form green ceramic bodies. In particular, EPD has been used by Sarkar, Haung and Nicholson (Electrophoretic deposition and its use to synthesize Al.sub.2 O.sub.3 /YSZ micro-laminate ceramic composites, Ceram. Eng. Sci. Proc. vol. 14 pp. 707-716 (1993)) to deposit laminated composites of alumina and yttria-stabilized zirconia (YSZ).
Conventional ceramic dental appliances, such as crowns, artificial teeth and bridges consist of a metallic base covered with ceramic layers. All-ceramic (i.e., metal-free) dental appliances are highly desirable because they match the appearance of natural teeth better than metal-ceramic crowns do, they enable X-ray examination through the appliance and are more biocompatible, avoiding gum inflammations and allergic reactions.
Existing techniques for fabrication of all-ceramic dental appliances, the best known being the "Vita in-Ceram" method, are based on a manual slip cast process which requires high skills and does not exclude the formation of pinholes in the appliances prepared.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method of EPD that can be used in the fabrication of small, precisely shaped ceramic bodies such as dental appliances, connecting ferrules, orifices and micro-tubes. Specifically, it would be highly advantageous to have a method of EPD that can be used in the fabrication of all-ceramic dental appliances